Hydrothermal synthesis and gas sensing characters of ZnO nanorods

ZnO nanorods are prepared by a hydrothermal process with cetyltrimethylammonium bromide (CTAB) and zinc powder at 182 °C. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The gas sensing properties of the materials have been investigated. The results indicate that the as-prepared ZnO nanorods show much better sensitivity and stability than the conventional materials. The PdO doping can improve the sensitivity and selectivity of the sensors. ZnO nanorods are excellent potential candidates for gas sensors.     

Fabrication and gas-sensing properties of hierarchically porous ZnO architectures

Hierarchically three-dimensional (3D) porous ZnO architectures are synthesized by a template-free, economical aqueous solution method combined with subsequent calcination. First, the precursors of interlaced and monodisperse basic zinc nitrate (BZN) nanosheets are prepared. Then calcination of the precursors produces hierarchically 3D porous ZnO architectures composed of interlaced ZnO nanosheets with high porosity resulting from the thermal decomposition of the precursors. The products are characterized by X-ray diffraction, thermogravimetric-differential thermalgravimetric analysis, scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller N₂ adsorption-desorption analyses. The BET surface area of the hierarchically porous ZnO nanostructures was calculated to be 12.8 m² g⁻¹. Compared with ZnO rods, the as-prepared porous ZnO nanosheets exhibit a good response and reversibility to some organic gases, such as ethanol and acetone. The responses to 100 ppm ethanol and acetone are 24.3 and 31.6, respectively, at a working temperature of 320 °C. These results show that the porous ZnO architectures are highly promising for gas sensor applications, as the gas diffusion and mass transportation in sensing materials are significantly enhanced by their unique structures. Moreover, it is believed that this solution-based approach can be extended to fabricate other porous metal oxide materials with a unique morphology or shape.     

Improved selective acetone sensing properties of Co-doped ZnO nanofibers by electrospinning

Pure and Co-doped (0.3 wt%, 0.5 wt%, and 1 wt%) ZnO nanofibers are synthesized by an electrospinning method and followed by calcination. The as-synthesized nanofibers are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) spectroscopy. Comparing with pure ZnO nanofibers, Co-doped nanofibers exhibit improved acetone sensing properties at 360 °C. The response of 0.5 wt% Co-doped ZnO nanofibers to 100 ppm acetone is about 16, which is 3.5 times larger than that of pure nanofibers (about 4.4). The response and recovery times of 0.5 wt% Co-doped ZnO nanofibers to 100 ppm acetone are about 6 and 4 s, respectively. Moreover, Co-doped ZnO nanofibers can successfully distinguish acetone and ethanol/methanol, even in a complicated ambience. The high response and quick response/recovery are based on the one-dimensional nanostructure of ZnO nanofibers combining with the Co-doping effect. The selectivity is explained by the different optimized operating temperatures of Co-doped ZnO nanofibers to different gases.     

Synthesis and gas sensing properties of bundle-like α-Fe2O3 nanorods

Bundle-like α-Fe₂O₃ nanostructures were successfully synthesized by a simple calcination of β-FeOOH precursor derived from a hydrothermal method in the presence of poly(vinyl pyrrolidone). The as-prepared products were characterized by X-ray power diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The results indicated that bundle-like nanostructures were composed of well-aligned single crystalline nanorods with the diameters of 20-30 nm and the lengths of 200-300 nm. The gas sensing properties of as-prepared products were investigated. It was found that the sensor based on α-Fe₂O₃ nanostructure exhibited high response, quick response-recovery, and good repeatability to acetone at 250 °C.     

Investigation on formaldehyde gas sensor with ZnO thick film prepared through microwave heating method

ZnO nanopowders were prepared through microwave heating method. ZnO thick film sensors were fabricated by using ZnO nanopowders as sensing materials. The phase composition and morphology of the material particles were characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The gas-sensing properties of the sensors based on ZnO nano-materials were investigated. It was found that the sensor based on ZnO nano-materials (low power, 10× 10 min) exhibited very high responses to benzene and toluene when operating at 440 and 370 °C, respectively; but the sensor based on ZnO (low power, 10× 10 min) showed very low responses to benzene and toluene when operating at 205–215 °C. The sensor based on ZnO (low power, 10× 10 min) showed high response and good selectivity to dilute formaldehyde when operating at 210 °C; especially, the response to 0.001 ppm HCHO attained 7.4 when operating at 210 °C.     

Ethanol gas sensor based on Al-doped ZnO nanomaterial with many gas diffusing channels

ZnO nanomaterial with multi-microstructures is synthesized by using normal pressure thermal evaporation and then doped with different Al₂O₃ contents by grinding in an agate mortar. The as-prepared Al-doped ZnO nanomaterials are characterized by X-ray diffraction and scanning electron microscopy. The characterization results show that all the compounds are wurtzite with hexagonal structure and are well crystallized. Channels/connecting holes arising from many kinds of ZnO microstructures are abundant. Both annealing and Al₂O₃-doping contributes to an increase in the quasi-one-dimensional and tri-dimensional microstructures. The as-prepared Al-doped ZnO nanomaterials show excellent gas responses to ethanol. The sensing mechanism of the ZnO-based nanomaterials with multi-microstructures is further analyzed by using the Effective Specific Surface Model. Excellent sensitivity (200) companied with short response time (8 s) and recovery time (10 s) to 3000 ppm ethanol is obtained with a ZnO-based sensor with 2 at.% Al₂O₃ at the operating temperature of 290 °C after the sensor is annealed at 500 °C.     

WO3 nanocrystals: Synthesis and application in highly sensitive detection of acetone

WO₃ nanocrystals have been prepared by a sol-gel route and characterized by X-ray diffractometry, scanning electron microscopy, and transmission electron microscopy. The experimental results show that WO₃ nanocrystals have a high crystallographic quality and a good dispersivity. The particles’ sizes are in the range of 25-100 nm. The fabricated WO₃ nanocrystal-based sensors have an excellent sensitivity and selectivity to acetone, and display a rapid response and recovery characteristics. The developed sensors exhibit a detection limit down to 0.05 ppm at 300 °C, rendering a promising application in noninvasive diagnosis of diabetes. The response mechanism of the WO₃ nanocrystal sensor to low concentration of acetone has been discussed based on the depletion layer model.     

LPG sensing properties of Pd-sensitized vertically aligned ZnO nanorods

One-dimensional (1-D) vertically aligned ZnO nanorods are synthesized on glass substrate through a simple chemical route and their liquefied petroleum gas (LPG) sensing properties are studied. The morphology and structure of vertically aligned ZnO nanorods has been characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The LPG sensing properties of the vertically aligned ZnO nanorods are improved significantly after palladium (Pd) sensitization. The unsensitized vertically aligned ZnO nanorods exhibited the maximum response of 37% at 573 K upon exposure to 2600 ppm LPG, which improved to 60% at operating temperature of 498 K after the Pd sensitization. The Pd-sensitized vertically aligned ZnO nanorods showed more selectivity towards LPG as compared to CO₂. Our results demonstrate that the chemically grown vertically aligned ZnO nanorods along with Pd sensitization are promising material for the fabrication of cost effective and high performance gas sensors.     

Gas sensing behavior of polyvinylpyrrolidone-modified ZnO nanoparticles for trimethylamine

Gas sensors based on polyvinylpyrrolidone (PVP)-modified ZnO nanoparticles with different molar ratios of Zn²⁺: PVP were prepared by a sol–gel method. Morphology of the sensors was characterized by field emission-scanning electron microscopy (FE-SEM), which indicated that the sensor with a molar ratio of Zn²⁺: PVP = 5:5 showed uniform morphology. Moreover, the sensor exhibited fairly excellent sensitivity and selectivity to trimethylamine (TMA). The response and recovery time of the sensor were 10 and 150 s, respectively. Finally, the mechanism for the improvement in the gas sensing properties was discussed.     

Thin film polypyrrole/SWCNTs nanocomposites-based NH3 sensor operated at room temperature

A PPY/SWCNTs nanocomposite-based sensor with relatively high sensitivity and fast response–recovery was developed for detection of NH₃ gas at room temperature. The gas-sensitive composite thin film was prepared using chemical polymerization and spin-coating techniques, and characterized by Fourier transformed infrared spectra and field-emission scanning electron microscopy. The results reveal that the conjugated structure of the PPY layer was formed and the functionalized SWCNTs were well-embedded. The effects of film thickness, annealing temperature, and SWCNTs content on gas-sensing properties of the composite thin film were investigated to optimize the gas-sensing performance. The as-prepared thin film PPY/SWCNTs composite sensor with optimized process parameters had a response of 26–276% upon exposure to NH₃ gas concentration from 10 to 800 ppm, and their response and recovery times were around 22 and 38 s, respectively.     

Electrospun Cu-doped ZnO nanofibers for H2S sensing

Pure and Cu-doped ZnO nanofibers were synthesized via electrospinning technology. The morphology and structure of the as-synthesized nanofibers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The effects of Cu doping on H₂S sensing properties at low concentration (1-10 ppm) were investigated at 230 °C. The results show that the H₂S sensing properties of ZnO nanofibers are effectively improved by Cu doping: 6 at% Cu-doped ZnO nanofibers show a maximum sensitivity to H₂S gas, and the response to 10 ppm H₂S is one order of magnitude higher than the one of pure ZnO nanofibers.     

Selective detection of HCHO gas using mixed oxides of ZnO/ZnSnO3

Mixed oxides of ZnO/ZnSnO₃ doped with Au element were prepared by a hydrothermal process. The crystal structure, composition and ceramic microstructure of the powders obtained were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results show that the product is the mixture of ZnO/ZnSnO₃; its particle size is about 500 nm with good dispersivity in shape. The sensitivity, selectivity, response and recovery properties of the ZnO/ZnSnO₃-based sensors were investigated by mixing a target gas in air. It is found that the sensors have remarkable sensitivity to HCHO vapor and satisfactory selectivity to other gases.     

沸石与CuO复合材料的气敏性能研究

采用水热合成法制备了花状CuO材料.为了改善CuO气体传感器性能,分别将ZSM-5型、HY型以及NaA型沸石与p型半导体CuO材料以涂覆法和直接混合法复合制成气敏元件.用X-射线衍射(XRD)、电子扫描显微镜(SEM)分别对制备的CuO材料以及3种沸石与CuO复合材料的形貌及其微观结构进行了表征与分析.将制备的几类敏感元件对多种VOC气体进行气敏测试.结果表明,与纯CuO相比,ZSM-5沸石/CuO复合材料均显著提高了对甲苯的响应值;HY沸石/CuO复合材料提高了对丙酮、乙醇、甲苯的响应值;NaA沸石/CuO复合材料改善了对乙醇和甲醛气体的响应值.初步分析了ZSM-5、HY、NaA沸石对CuO气敏特性改善的机理.     

Full band Monte Carlo calculations of velocity-field characteristics of wurtzite ZnO

The calculated results of electron transport properties of wurtzite ZnO with the full band Monte Carlo simulations are presented. The electronic band structure data being used in the simulations is based on the first-principles of total-energy pseudopotential method. The negative differential resistance effect in velocity-field characteristics of wurtzite ZnO was observed. At room temperature the threshold electric field is about 2.4×¹⁰⁵ V/cm, and the peak drift velocity is about 1.5×¹⁰⁷ cm/s. The electron mobility obtained in this work is approximately 285 cm²/Vs at room temperature.     

氧等离子体处理ZnO纳米纤维材料的制备及其对丙酮气敏性能的研究

采用静电纺丝法制备了ZnO纳米纤维材料并使用氧等离子体对其进行表面处理.通过X射线衍射(XRD),扫描电子显微镜(SEM),BET比表面积测试以及X射线光电子能谱分析(XPS)等手段对样品的结构与形貌进行了表征分析.将氧等离子体处理前后的ZnO纳米纤维分别制成气体传感器,对浓度为1×10-6~100×10-6(体积分数)丙酮气体的敏感特性进行了测试分析.测试结果表明,氧等离子体处理后的ZnO纳米纤维响应值较未处理的ZnO纳米纤维有大幅度的提升,最佳工作温度也有所降低,且对甲醛、苯、甲苯、二甲苯等几种干扰气体表现出更好的选择性.从晶粒间势垒和耗尽层厚度等角度初步分析了氧等离子体处理改善ZnO气敏特性的机理.     

Influence of sputtering power on properties of ZnO thin films fabricated by RF sputtering in room temperature

High mobility and c-axis orientated ZnO thin films were deposited on glass substrates using RF sputtering method at room temperature.Structural properties of ZnO thin films were investigated by X-ray diffraction (XRD).Surface morphology and roughness were studied with scanning electron microscopy (SEM) and atomic force microscopy (AFM).Electrical properties were measured at room temperature using a Hall effect measurement system.The influence of sputtering power on characteristics of ZnO thin films is studied.The results indicate that the sputtering powers have great influence on the crystal quality and mobility of ZnO thin films.By using optimized sputtering conditions,high crystal quality ZnO thin films with Hall mobility of 34 cm 2 /V·s at room temperature were obtained.     

Dispersive SnO2 nanosheets: Hydrothermal synthesis and gas-sensing properties

SnO₂ nanosheets with the thickness of 10 nm were successfully synthesized by a simple hydrothermal process at 180 °C for 12 h. The samples were characterized by X-ray power diffraction, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The sensor performance of the as-prepared SnO₂ nanosheets for ethanol and carbon monoxide was measured. The results indicate that the sensor exhibited high response, quick response-recovery kinetics, and good repeatability.     

Microwave assisted fast synthesis of various ZnO morphologies for selective detection of CO, CH4 and ethanol

ZnO nanocrystals with various morphologies were synthesized via a fast and facile microwave assisted method using zinc acetate as starting material, guanidinium and acetyl acetone as structure directing agents, and water as solvent. Reaction conditions, templates and pH of the reaction medium were adjusted in order to achieve nanorod, nanoparticle, and flower-like morphologies. As synthesized ZnO samples were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and nitrogen adsorption analysis (BET). Response and selectivity of the samples to CO, CH₄ and ethanol were measured in a flow system. It is shown that different morphologies of ZnO nanoparticles exhibit different responses and selectivities. Flower-like morphology is highly selective to CO, while nanorods and nanoparticles are selective to methane and ethanol, respectively. Moreover, in a wide range of temperatures, response of ZnO nanorods and nanoparticles towards CO is temperature independent.     

基于Al掺杂ZnO的丙酮气敏传感器以及紫外光激发对其气敏性能的影响

采用溶胶凝胶法制备的Al掺杂ZnO纳米粉末（AZO）。利用X射线衍射（XRD）和扫描电子显微镜（SEM）表征样品的晶体结构和表面形貌。采用浸渍提拉法将该样品制成旁热式气体传感器,检测其对不同气体的响应恢复特性。结果表明：Al掺杂ZnO表面粗糙,Al的掺杂能够抑制ZnO晶粒增长。当工作温度为70℃、湿度为27%RH时,4.98wt.%Al掺杂ZnO对丙酮气体具有很好的选择性,电阻灵敏度达到了14075,响应和恢复时间分别为1 s和3 s。紫外光照射可明显提高传感器的气敏特性,并降低工作温度。     

A vertical structure photodetector based on all‐inorganic perovskite quantum dots

In this work, the vertical structure photodetector based on CsPbBr₃ quantum dots (QDs) with a structure of indium tin oxide (ITO)/zinc oxide (ZnO)/CsPbBr₃ QDs/Au is reported. In this device, CsPbBr₃ QDs film works as the light‐harvesting layer, and ZnO QDs film acts as the electron transport channel, which can extract the electron efficiently and improve the quality of CsPbBr₃ QDs film. As a result, the on/off ratio, detectivity and rise time (decay time) of CsPbBr₃/ZnO hybrid photodetector are measured to be 2.4 × 10⁶, 2.25 × 10¹¹, and 62 milliseconds (82 ms) under 0‐V bias. This work inspires the development of vertical structure photodetectors based on the all‐inorganic perovskite QDs.